1. Field of the Invention
The present invention relates to an image processing device and, more particularly, to an image processing device such as an optical sensor, liquid crystal display, or plasma display for reading or displaying image information.
2. Related Background Art
An X-ray examination apparatus used in the medical field employs, as a mainstream, a scheme of converting an X-ray into visible light by a fluorescent plate and exposing a film in contact with the fluorescent plate to the light for confirmation because a morbid portion of a patient must be accurately detected. In fact, the following problems are pointed out in association with this confirmation method: it takes a time from measurement to diagnosis although the resolution of an image has no problem for practical use, and specifying a measurement position (e.g., morbid portion) greatly depends on the skill and intuition of the technician.
In recent years, large area sensors using amorphous silicon diodes have been developed and increased in their reliability. When amorphous silicon is used, the area can be easily increased. Along with this advantage, an urgent demand has arisen for developing a device for increasing the efficiency of the conventional X-ray examination for diagnosing a morbid portion of a patient by using an emphasized image processed in real time. To largely change the panel formation process size at once to achieve a large area sensor, new investment for plants and equipment for the film formation and photo-process is impractically required. Hence, actually, a plurality of panels having an existing process size are two-dimensionally bonded in accordance with the pixel pitch.
FIG. 1 is a schematic sectional view showing an X-ray sensor manufactured by bonding. Referring to FIG. 1, each sensor panel 301 comprises a board made of non-alkali glass or the like. A base 302 fixes four sensor panels 301 at predetermined positions and has an X-ray absorption lead member for protecting an electrical mounted portion on the lower surface. A first bonding layer 303 bonds the sensor panels 301 to the base 302. A fluorescent plate 305 serves as a wavelength conversion member for converting an X-ray into visible light. A gel-like second bonding layer 304 bonds the fluorescent plate 305 to the sensor panels 301. Printed circuit boards 307 electrically drive the sensor panels 301, respectively. Flexible wiring boards 306 connect the printed circuit boards 307 to the sensor panels 301, respectively. The members 301 to 307 form an X-ray sensor portion 330.
The X-ray sensor also has a case 320, a lid 321, a cover 323 formed from, e.g., lead to protect the electrical mounted portion, legs 324 for fixing the printed circuit boards 307, and angles 325 for fixing the base 302 to the case 320. The members 320 to 325 form a chassis portion 340. The X-ray sensor unit is formed by fixing the X-ray sensor portion 330 in the chassis portion 340.
An X-ray incident from the upper side in FIG. 1 as image information is converted into a visible light wavelength by the fluorescent plate 305, transmitted through the transparent second bonding layer 304, and is incident on optical sensor elements (photoelectric conversion elements) two-dimensionally arrayed on the upper surface of each sensor panel. The incident light is converted into an electrical signal by the optical sensor elements and converted into image information by the printed circuit boards 307 through the flexible wiring boards 306, so the X-ray sensor functions as a two-dimensional X-ray sensor.
A technical point that must be taken into consideration in selecting the structure of such a two-dimensional X-ray sensor is that the four sensor panels need be accurately aligned relative to each other in the planar direction to ensure a high resistance to mechanical impact in bonding the fluorescent plate because of the small pixel pitch. Usually, for the first bonding layer 303, a silicone-based cold-setting adhesive, which rarely expands/shrinks in hardening and has a strong adhesion and elasticity after hardening is used.
A normal temperature guarantee range of an X-ray sensor is xe2x88x9230xc2x0 C. to +50xc2x0 C. The technical problem described in the prior art must be solved within this temperature range. However, in this structure, since the thermal expansion coefficient of the sensor panel 301 as 4.7xc3x9710xe2x88x926/xc2x0 C. and that of the base 302 as 2.9xc3x9710xe2x88x925/xc2x0 C. have a large difference (this difference normally appears in use of the above-described materials), and therefore, the difference in expansion/shrinkage due to the temperature difference of 80xc2x0 C. is as large as 617%. When the outer size of each sensor panel 301 is 250 mm, the expansion/shrinkage difference of 486 xcexcm directly appears as a pixel pitch shift because of the elastic force of the adhesive 303. When the pixel pitch of the X-ray sensor is 160 xcexcm, this shift amount cannot be neglected. In addition, when the sensor panel 301 and base 302 have the same thickness in terms of mechanical strength, they largely warp. When the base 302 has a sufficient thickness in terms of mechanical strength with respect to the sensor panel 301, large internal stress is generated in the sensor panel to degrade the characteristics of the element and also peel the adhesive 303. This tendency becomes conspicuous as the screen size increases.
It is an object of the present invention to provide a structure for suppressing a pitch shift between bonded sensor panels or opposing panels particularly in an image processing device having a large screen even when the temperature changes.
It is another object of the present invention to provide a structure for suppressing warp, internal stress, and peeling in bonded panels.
It is still another object of the present invention to provide an inexpensive image processing device having excellent cost performance and an arrangement capable of facilitating selection of materials to be used and proper design and shortening the development period.
It is still another object of the present invention to provide an image processing device having at least one first board having a thermal expansion coefficient a and a plurality of semiconductor elements or/and wiring lines at an equal pitch P, and a second board having a thermal expansion coefficient b and opposing and bonded to the first board through bonding means,
wherein letting L be a length of the first board in a direction of array of the semiconductor elements or/and the wiring lines on the first board opposing the second board and T be a width of a temperature guarantee range of the image processing device,
xe2x88x92P/2 less than LT(axe2x88x92b) less than P/2
is satisfied.
According to the present invention, even when the temperature changes, the pixel pitch shift between the first panel and second panel which oppose and are bonded to each other or relative pixel pitch shift between the plurality of first panels can be prevented or minimized. In addition, warp or internal stress can be suppressed, and peeling can be prevented.
According to the present invention, a design concept capable of preventing or avoiding problems posed by a change in temperature due to a change in use conditions or the like can be provided.
According to the present invention, an image processing device which can be designed in a shorter developing period and has more excellent cost performance because materials to be used can be appropriately selected in accordance with the required performance and cost can be provided.